Abstract:

On fine days，photosynthetic characteristics of the leaves at different positions in three safflower varieties were monitored using portable LI-6400 photosynthesis system, and correlations between the net photosynthesis rate and the yield, agronomical characters were analyzed within 16 safflower varieties from 7 different countries. The results showed that maximum photosynthesis rate (P_nmax), light compensation point (LCP), light saturation point (LSP), dark respiration rate (Rd), apparent quantum yield (AQY) were in upper leaves > in middle leaves > in lower leaves. Light- photosynthesis curves indicated that the photosynthetic rate of all the leaves decreased significantly under the high light intensity except the upper leaves of PI 401470 and Chuanhong 1. And under the low light intensity, there was no marked difference between the photosynthetic rates of the leaves at the different positions. when the PFD exceed 400µmolm^-2 s^-1, the photosynthetic rate of the upper leaves was significantly higher than that of the lower ones. The diurnal variation pattern of photosynthesis was different in the leaves at the different positions and in different varieties , the time to the peaks and the value of the peaks were also different. The upper leaves of PI 401470 and Chuanhong 1 showed a single-peak curve, and the others showed a double-peak curve. Diurnal changes of the photosynthetically available radiation, air temperature, relative humidity, vapor pressure deficit and CO₂ concentration in the air all showed a one-peak curve. The analysis of the upper leaves at flower bud stage showed that P_n had significant or highly significant positive correlations with flower yield per plant, 100-seed weight and the diameter of top fruitball. Safflower breeding for high photosynthetic efficiency would be an effective way for improving the yield.

Key words: Safflower, Photosynthesis, Yield